Israeli Prime Minister Benjamin Netanyahu speaks during the 68th session of the General Assembly at United Nations headquarters on Oct. 1. (Seth Wenig / AP)

Israeli Prime Minister Benjamin Netanyahu warned United Nations delegates Tuesday that to avoid a military conflict they must stand firm in putting pressure on Iran to open up its nuclear program to inspection.

“Iran wants to be in position to rush forward and build nuclear bombs before the world can prevent it,” Netanyahu said, warning that recent gestures from Iran toward peace are a “ruse” to lull the West into backing off.

He said the “one big problem” that stands in in the way of Iran’s aims are the economic sanctions that the West has imposed to get Iran to prove its claim the its nuclear program is for peaceful purposes. He warned that the sanctions must remain and be toughened if Iran is to be stopped.

“A nuclear armed Iran would have a choke-hold on the world’s main energy supplies, it would trigger nuclear proliferation throughout the Middle East,” he said. “It would make the specter of nuclear terrorism a clear and present danger.”

And if talks fail, Netanyahu left little doubt that Israel will take matters into its own hands.

“Israel will not allow Iran to get nuclear weapons,” he said. “If Israel is forced to stand alone, Israel will stand alone.”

His speech comes after Iranian President Hasan Rouhani brought a new message of friendliness during a four-day trip to the United Nations in New York last week, a trip that ended with a 15-minute phone call with Obama. It was the first phone call between two leaders from the U.S. and Iran in three decades.

U.S. Secretary of State John Kerry and other world powers will participate in talks with Iran over curtailing its nuclear program later this month.

But Iran on Tuesday complained that Obama’s recent statements while meeting with Netanyahu at the White House on Monday have harmed prospects for peace.

Foreign Minister Mohammad Javad Zarif said on Iranian television that Netanyahu’s warnings that Iran’s nuclear ambitions aim at building a bomb for Israel’s destruction are lies and show Netanyahu is the “most isolated man in the U.N.”

“We have seen nothing from Netanyahu but lies and actions to deceive and scare, and international public opinion will not let these lies go unanswered,” Zarif said on Iranian television, according to an AFP report.

Zarif also knocked President Obama for saying that while the United States seeks a diplomatic solution to the standoff, it has not dismissed more forceful measures, including military action. Such talk amounts to a flip-flop after the friendliness exhibited last week, Zarif said on Twitter.

“President Obama needs consistency to promote mutual confidence,” he said in a tweet. “Flip-flop destroys trust and undermines U.S. credibility.”

Obama on Friday had welcomed the Iranian president’s overtures and pledge not to seek nuclear weapons for military purposes, and he mentioned in his speech at the United Nations that Iran’s Supreme Leader Ali Khamenei, “has issued a fatwa against the development of nuclear weapons.”

However, a Middle East research group based in Washington says there is no evidence that such an edict exists.

“An exhaustive search of the various official websites of Iranian Supreme Leader Ali Khamenei turned up no such fatwa, either on his fatwa website or on his personal website,” according to the Middle East Media Research Institute, which tracks and translates news and official reports from the region.

MEMRI says the fatwa was first mentioned by Sirius Naseri, an Iranian representative to a meeting of the U’N.’s nuclear agency in 2005, but is not listed among the hundreds of fatwas that Khamenei has issued on his official or personal website.

Netanyahu, who served as Israel’s ambassador to the U.N. from 1984 to 1988, said that oil-rich Iran has no reason to pursue nuclear technology other than to build a bomb, as Rouhani claimed, and he listed reasons to think that it is.

He told Obama during a visit to the White House Monday that despite the change in tone, “Iran is committed to Israel’s destruction. So for Israel, the ultimate test of a future agreement with Iran is whether or not Iran dismantles its military nuclear program.”

In Israel, Ya’acov Shani, a 66-year-old Jerusalemite having a coffee at Café Ne’eman, a local bakery-café, was not optimistic about getting Iran to end its threat.

“Obama is using this opportunity to avoid a conflict with Iran. The problem is, while Obama is negotiating over Iran’s nuclear capability, Iran will in fact be developing weapons of mass destruction,” Shani said.

Mahmoud Issa, an Arab resident of Bethlehem, in the West Bank, who stopped at a Jerusalem gas station to sit and talk with some friends before heading home, had worry beads in his hand.

“I think Obama and Bibi (Netanyahu) should give the nuclear talks with Iran a chance. Force should be a last resort, not a first choice. I’m praying for peace for everyone in the region, both Jews and Arabs.”

But he also wondered whether it was not OK for Iran to have nuclear weapons.

“If the U.S. and Israel and other nations have these weapons, why, in theory, shouldn’t an Arab country have one? I have four children and I can’t give food and an education to one child and not another.”

Standing in the convenience store his family owns, 25-year-old Lior Huga said:

“I think Obama is on the right path. I hope so, anyway. Negotiations are better than military action. But that won’t work unless Iran’s promises are thoroughly verified and that its ability to develop nuclear weapons is eliminated.”

He said Netanyahu “has no choice but to go along with Obama’s approach to Iran and Syria. He can’t oppose the U.S. administration. Israel needs it.”